The present invention relates to an air quantity regulating apparatus for air conditioning and, more particularly, to an air quantity regulating apparatus disposed in the vicinity of a supply opening of a zone in an air conditioning system for supplying conditioned air to a plurality of zones from a single air conditioner through a duct.
In an air conditioning system of the type described above, pressure loss of air from the air conditioner to the zones is not constant. An air quantity regulating apparatus disposed in the vicinity of the supply opening of each zone changes the quantity of air so as to regulate a zone temperature in response to a room thermostat signal, thereby changing the pressure in the duct which supplies the air. The air quantities at all supply openings are influenced by the difference between pressures at various locations in the duct and by a change or fluctuation in the pressure at a single location in the duct. This impedes the designed distribution and regulation of the air quantity. Since the system described above is used to regulate room temperature by air, a minimum ventilating quantity must be assured independently of room temperature, and the concentration of hazardous gases such as CO.sub.2 and CO must be kept within the rated standards. Furthermore, along with air conditioning, heating and cooling must be equally performed.
A room thermostat generally produces an output in response to a difference between the preset thermostat temperature and the actual room temperature. When the room temperature is higher than the preset temperature in the cooling mode, the air quantity regulating apparatus must serve to increase the air quantity currently supplied and to lower the room temperature. However, in the heating mode, the air quantity regulating apparatus must serve to decrease the air quantity and to lower the room temperature under the same conditions as in the cooling mode. Therefore, a changeover function is required which inverts the thermo signal when the cooling mode is changed to the heating mode and vice versa.
In order to solve the conventional problems such as a difference between pressures in the duct and a change in pressure in the duct, systems were developed and disclosed in Japanese Utility Model Publication Nos. 48-5294 and 48-29245 and U.S. Pat. No. 3,403,852.
In these conventional air quantity regulating apparatuses, a spring is provided to control the internal resistances corresponding to static pressure components, respectively. The throttle valve is biased by the biasing force of the spring so as to obtain a pressure difference between the upstream portion and the downstream portion of the throttle valve, thereby achieving a constant air quantity function (for supplying the constant air quantity independently of a pressure difference in the duct and a change in pressure in the duct).
However, the conventional air quantity regulating apparatuses must have a large pressure-receiving portion to operate the throttle valve against the biasing force of the spring. Accordingly, the pressure-receiving portion itself forms a hindrance to the air flow. As a result, the minimum operating pressure against the biasing force of the spring is high, and the apparatus as a whole becomes large. A conventional air quantitiy regulating apparatus is also known which uses a bellows diaphragm. However, in an apparatus of this type, the minimum operating pressure cannot be decreased. If the minimum operating pressure is to be decreased, the bellows diaphragm becomes very large. Since these conventional apparatuses do not have a changeover function, the contact point of the room thermostat must be adjusted to the corresponding one to be inside the thermostat or at a position spaced apart therefrom when the cooling mode is changed to the heating mode and vice versa.
A large blower motor and a separate control unit for the changeover function are required, which are both incompatible with the recent trend towards automation and energy conservation.
Apparatuses for changing the air quantity in order to control room temperature have been developed, as disclosed in U.S. Pat. Nos. 3,687,364 and 4,147,298.
These conventional apparatuses have an air quantity detector, so that their minimum operating pressure is lower than that of any other conventional apparatus. In the above apparatuses, air quantitity detection is utilized to determine the closed position of the throttle valve. Such detection is not used to provide the constant air quantitity function. Therefore, the conventional apparatuses cannot compensate for the difference of pressures in the duct and the change in pressure in the duct, thus temporarily resulting in excessive air quantity or lack of air quantity. This indicates that room temperature control cannot be stably performed, and hunting is repeated at predetermined intervals. Also, when an excessive quantity of air is supplied from the supply opening, it may cause considerable noise. In the same manner as in the conventional apparatus having a constant air quantity function, the changeover function is realized only by changing the position of the contact point of the room thermostat. At the same time, the throttle valve must be mechanically stopped so as not to fully close the valve so that the minimum ventilating quantity must be guaranteed. It is also impossible to compensate for the difference of pressures in the duct and the change in pressure in the duct.
In the conventional apparatuses, pneumatic control techniques are more common than any other technique. These pneumatic control techniques are then applied to electric control systems. In pneumatic control, the air quantity is obtained in proportion to a room load. However, when pneumatic control is applied to electric control, the intermediate control position cannot be readily set. Therefore, pneumatic control cannot be satisfactorily utilized for an air quantity regulating apparatus for electric control. Along with the strong demand for energy conservation, it is desired that an air quantity regulating apparatus for the electric control be developed which meets a variety of applications.